Re: faster boots?

[dean gaudet]

On Thu, 4 Apr 2002, Andrew Morton wrote:

> I guess the greatest benefit would come from reorganising the
> layout of the root filesystem's data and metadata so the
> pagecache prepopulation doesn't have to seek all over the place.

windows xp does this automatically (but it takes a lot of idle time before
it'll start playing with your disk)... search for "bootvis" at
microsoft.com, that tool can force the reorganization to occur.  it's
worth 10%ish there as well (quite noticeable on laptops).  they appear to
reorganize the boot-time files into one big contiguous region.  that's
fetched into their equivalent of the page cache with sequential reads.

it's certainly interesting theory -- trying to do disk layout which is
optimised for particular access patterns... it's kind of a hack to do this
just for boot time, but definitely educational :)

in some ways, the filesystem is the wrong place to do this type of
activity -- you could approach the problem as a block layer device between
the fs and the hardware which maintains statistics on access patterns and
moves blocks around to optimise access time -- which lets you fix all
sorts of seeking problems.  i guess the challenge would be maintaining a
map of logical block number to physical block number.  hmm.  guess that's
kind of hard.

-dean